Electric machines must be cooled in order to provide the following: controlling the thermal load, maintaining adequate material strength, and avoiding the expansion of components which is too great and the problem of thermal stresses associated therewith.
Electric motors have been suggested which are equipped with stators having a plurality of cooling channels passing therethrough. Such configurations are expensive. Other suggestions are based on liquid cooling within the armature shaft. As a rule, this requires external coolant pumps. For this reason, an impeller pump for the purpose of driving a coolant is mounted in the hollow armature shaft, for example, as disclosed in German Patent 4,020,416.
International Class H 02 K 9/19 includes cooling and ventilating systems for machines having a closed housing and with a closed circulating system connected thereto. The closed circulating system utilizes a liquid coolant.
German patent publication 2,124,463, for example, discloses a hermetically closed electric motor which is located in a cylindrical compartment having an inlet opening and an outlet opening for the coolant.
The electric motor disclosed in German patent publication 2,331,493 includes a closed housing which is surrounded by an annular chamber through which coolant flows.
The subject matter of German Patent 3,545,665 likewise discloses a liquid-cooled electric motor having a pot-shaped housing over which a pot-shaped casing is mounted. The casing includes an inlet and an outlet for a coolant liquid which circulates between the housing and the casing.
A problem in such electric motors which has not yet been solved is especially that the tightness can only be achieved with difficulty for temperature fluctuations which are to be dealt with. The electric motor is built into a closed compartment and, additionally for this reason, the electric motor is accessible for maintenance and repair work only after a complete disassembly of the cooling chamber.
Overall, the known cooling chambers are complex and are therefore expensive with respect to their manufacture.
Japanese patent publication 64/136002 describes a cooling vessel which is made of a material having good heat conducting capability such as metal. As shown in the drawing, the cooling vessel has a hollow-cylindrical configuration so that it can be pushed over a motor which is correspondingly configured to be hollow cylindrical.
The metal used is usually hardly flexible and therefore is not suited to assume an intimate contact with various different forms. The cooling cylinder in this publication is possibly somewhat resilient because it is a hollow cylinder having longitudinal slits. The combination of longitudinal slits and spring action is however not suitable to be in close intimate contact with complicatedly configured forms having projections and the like.
The cooling arrangement disclosed in U.S. Pat. No. 4,213,498 is a simple flexible and only slightly expandable heat exchanger made of plastic. Liquid flows through the heat exchanger which is configured so that it conforms to the outer cylindrical surface of tanks or the like.
U.S. Pat. No. 4,971,144 is directed to a cooling wrap. The cooling wrap disclosed in both United States patents includes an upper layer and a lower layer and a channel system disposed therebetween. The distance between the upper and lower layers is fixed by this channel system.
The heat exchanger of U.S. Pat. No. 4,213,498 is made of plastic such as polypropylene or polyethylene. The heat exchanger is flexible but the plastic material is only slightly expandable. Because of the slight expandability of the materials and because of the configuration of the heat exchanger with a constant spacing between lower and upper layers, the heat exchanger is only suitable for cylindrically-shaped surfaces such as vessels and tanks. Semicircular or other surfaces having reliefs cannot be in intimate contact over the entire surface thereof with exchangers of this type.